The serine proteases (SP) are a large family of proteolytic enzymes that include the digestive enzymes, trypsin and chymotrypsin, components of the complement cascade and of the blood-clotting cascade, and enzymes that control the degradation and turnover of macromolecules of the extracellular matrix. Serine proteases are so named because of the presence of a serine residue in the active catalytic site for protein cleavage. Serine proteases have a wide range of substrate specificities and can be subdivided into subfamilies on the basis of these specificities. The main sub-families are trypases (cleavage after arginine or lysine), aspases (cleavage after aspartate), chymases (cleavage after phenylalanine or leucine), metases (cleavage after methionine), and serases (cleavage after serine).
Most proteases are secretory proteins which contain N-terminal signal peptides that serve to export the immature protein across the endoplasmic reticulum and are then cleaved (von Heijne (1986) Nuc. Acid. Res. 14: 5683–5690). Differences in these signal sequences provide one means of distinguishing individual serine proteases. Some serine proteases, particularly the digestive enzymes, exist as inactive precursors or preproenzymes, and contain a leader or activation peptide sequence 3′ of the signal peptide. Typically, this activation peptide may be 2–12 amino acids in length, and it extends from the cleavage site of the signal peptide to the N-terminal IIGG (SEQ ID NO:76) sequence of the active, mature protein. Cleavage of this sequence activates the enzyme. This sequence varies in different serine proteases according to the biochemical pathway and/or its substrate (Zunino et al. (1988) Biochimica et. Biophysica Acta 967: 331–340; Sayers, et al. (1992) J. Immunology 148: 292–300). Other features that distinguish various serine proteases are the presence or absence of N-linked glycosylation sites that provide membrane anchors, the number and distribution of cysteine residues that determine the secondary structure of the serine protease and the sequence of a substrate binding sites such as S′. The S′ substrate binding region is defined by residues extending from approximately +17 to +29 relative to the N-terminal I (+1). Differences in this region of the molecule are believed to determine serine protease substrate specificities (Zunino et al, supra).
Numerous disease states are caused by and can be characterized by alterations in the activity of specific proteases and their inhibitors. For example emphysema, arthritis, thrombosis, cancer metastasis and some forms of hemophilia result from the lack of regulation of serine protease activities (see, for example, Textbook of Biochemistry with Clinical Correlations, John Wiley and Sons, Inc. N.Y. (1993)). In case of viral infection, the presence of viral proteases have been identified in infected cells. Such viral proteases include, for example, HIV protease associated with AIDS and NS3 protease associated with Hepatitis C. These viral proteases play a critical role in the virus life cycle.
A series of serine proteases have been identified in murine cytotoxic T-lymphocytes (CTL) and natural killer (NK) cells. These serine proteases are involved with CTL and NK cells in the destruction of virally transformed cells and tumor cells and in organ and tissue transplant rejection (Zunino et al. (1990) J. Immunol. 144: 2001–2009; Sayers et al. (1994) J. Immunol. 152: 2289–2297). Human homologs of most of these enzymes have been identified (Trapaniet et al. (1988) Proc. Natl. Acad. Sci. 85: 6924–6928; Caputo et al. (1990) J. Immunol. 145: 737–744).
Proteases have also been implicated in cancer metastasis. Increased synthesis of the protease urokinase has been correlated with an increased ability to metastasize in many cancers. Urokinase activates plasmin from plasminogen which is ubiquitously located in the extracellular space and its activation can cause the degradation of the proteins in the extracellular matrix through which the metastasizing tumor cells invade. Plasmin can also activate the collagenases thus promoting the degradation of the collagen in the basement membrane surrounding the capillaries and lymph system thereby allowing tumor cells to invade into the target tissues (Dano, et al. (1985) Adv. Cancer. Res., 44: 139).
The discovery of a new serine protease precursor and the polynucleotides encoding it satisfies a need in the art by providing new prognostic and diagnostic diagnostic methods and, therapeutic compositions useful in the treatment or prevention of cancer.